The invention relates to an arrangement for generating an X-ray or gamma beam with small cross-section and variable direction, having an X-ray or gamma emitter, from the focus of which a bundle of rays emerges, and a diaphragm arrangement, which cuts out a beam from the bundle of rays and comprises a rotatable hollow-cylindrical first diaphragm body having two mutually offset helical slits on the circumference.
Of interest is commonly owned copending application entitled "Device for Forming an X-ray or Gamma Beam of Small Cross-Section and Variable Direction" Ser. No. 400,188 filed Aug. 29,1989 in the name of G. Harding.
Arrangements of this type are essentially known from European laid-open patent application 74,021 for medical applications and from German Offenlegungsschrift 3,443,095 corresponding to U.S. Pat. No. 4,750,196 for industrial applications. The diaphragm body of a radiation-absorbing material has in this case the form of a hollow cylinder which is provided on its circumference with two mutually offset helically encircling slits. If a bundle of parallel rays falls onto such a diaphragm body perpendicularly to its cylinder axis, there is always a point at which an X-ray beam passes through the two slits. If the diaphragm body is turned, this point shifts along the axis, so that a periodically moved X-ray beam emerges behind the diaphragm body. This periodically moved X-ray beam can be used for medical or industrial examinations.
An X-ray beam with trapezoidal cross-section is defined by the two slits in the diaphragm body. What is desired, however, is a square or a circular cross-section, producing a directionally independent spatial resolution. With the same width of the two slits, the approximation to a square cross-sectional shape is all the better the larger the angle by which the two slits intersect each other. A larger angle of intersection could be achieved by using a diaphragm body with large diameter and small axial length. For many applications, however, a relatively large angle of deflection of the X-ray beam is necessary, which necessitates a corresponding axial length of the diaphragm body; a large diameter is undesirable in many applications due to the associated unit volume.